With Hurricane Sandy churning toward New York, Westchester County Executive Rob Astorino said mandatory evacuations are under way in some low-lying areas along the Long Island Sound and warned county residents to stay indoors.

Flanked by staff and members of the county's emergency management team, the county executive said towns and villages are already experiencing some flooding and said local governments have told people to evacuate those areas.

"This is a dangerous storm," Astorino told reporters at a news conference at the county's emergency management center at the State Police barracks in Hawthorne. "It's no time to be a hero or a thrill seeker. It's important that people heed the warnings. If there are problems later, we may not be able to get you."

Astorino said county officials are most concerned about the low-lying neighborhoods along the Sound Shore, such as Rye and Mamaroneck, and Hudson River communities, such as Yonkers and Dobbs Ferry, which could experience widespread flooding Monday evening. High tide was expected at midnight, which they said would bring another surge of 6 to 11 feet.

The villages of Mamaroneck and Port Chester have called for mandatory evacuations in some neighborhoods.

Astorino said about 50 members of the National Guard were on standby. He has also authorized additional police patrols throughout the county and called up water rescue teams in case they are needed.